Problem

The Clojure and ClojureScript readers do not currently track the column number when reading forms, only line numbers.

((juxt :line :column) (meta #'identity)) => [1351 nil]

Several components could be improved by tracking column information:

Compiler error messages

Tooling, such as SLIME or IDEs (consider jump-to-definition)

However, the key motivator is Source Maps for ClojureScript. The development tools in modern browsers have growing support for graphical debugging of machine generated code. This is relevant for minified JavaScript, but it's also intended for use with multi-stage transformations, such as CoffeeScript/GWT/ClojureScript -> Unoptimized Javascript -> Google Closure Compiler -> Final JavaScript